<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>计算器</title>
	<script type="text/javascript">
		window.onload = function(){

			var oInput01 = document.getElementById('input01');
			var oInput02 = document.getElementById('input02');
			var oFuhao = document.getElementById('fuhao');
			var oBtn = document.getElementById('btn');		


			oBtn.onclick = function(){

				var num01 = oInput01.value;
				var num02 = oInput02.value;
				var fuhao = oFuhao.value;

				if(num01=="" || num02==""){
					alert('输入框不能为空！');
					return;
				}

				if(isNaN(num01) || isNaN(num02)){
					alert('请输入数字！');
					return;					
				}


				switch(fuhao){

					case '0':
						alert((parseFloat(num01)*100+parseFloat(num02)*100)/100);
						break;
					case '1':
						alert((parseFloat(num01)*100-parseFloat(num02)*100)/100);
						break;
					case '2':
						alert(((parseFloat(num01)*100)*(parseFloat(num02)*100))/10000);
						break;
					case '3':
						alert((parseFloat(num01)*100)/(parseFloat(num02)*100));
						break;
				}				

			}





		}




	</script>
</head>
<body>
	<h1>计算器</h1>
	<input type="text" name="" id="input01">
	<select id="fuhao">
		<option value="0">+</option>
		<option value="1">-</option>
		<option value="2">*</option>
		<option value="3">/</option>
	</select>
	<input type="text" name="" id="input02">
	<input type="button" name="" value="计算" id="btn">
</body>
</html>